A conventional dual lever type derailleur gear unit for a bicycle comprises a wire carrying wheel rotatably mounted on a supporting base for moving a derailleur wire so as to control the pivot motion of a front derailleur (or a rear derailleur) of the bicycle, a ratchet wheel fixedly engaged with the wire carrying wheel for rotating it, a first shifting lever provided for rotating the ratchet wheel together with the wire carrying wheel along one direction so as to tension the derailleur wire, a second shifting lever provided for rotating the ratchet wheel together with the wire carrying wheel along a reverse direction so as to release the derailleur wire, and a plurality of ratchet mechanisms for controlling the normal and reverse rotation of the ratchet wheel.
By such an arrangement, however, the construction of such a conventional dual lever type derailleur gear unit is complicated, thereby causing an inconvenience in assembling and maintenance.
The present invention has arisen to mitigate and/or obviate the disadvantage of the conventional treadmill.